Method of making pressure vessels and the like



Oct. 12, 1943. e. RAYMOND ETAL METHOD OF MAKING PRESSURE VESSELS AND THELIKE Filed Aug. 20, 1941 3 Sheets-Sheet l ynne R0 and Merl 0 CltfC/I, Q4gag/z L, flea s, 9

INVENTORS 6w 1m ATTORNEY Oct. 12, 1943. s. RAYMOND ETAL METHOD OF MAKINGPRESSURE VESSELS AND THE LIKE Filed Aug. 20, 1941 3 Sheets-Sheet 2INYENTORS Gwyn/1c Raymond Merl 0. Cree fia/ M, 4 eagles,

ATTORNEY Oct. 12, 1943'. G RAYMOND ETAL 2,331,504

METHOD OF MAKING PRESSURE VESSELS AND THE LIKE Filed Aug. 20, 1941 3Sheets-Sheet 5 INVENTORS Gwyn/re Raymond UNITED STATES PATENT OFFICEMETHOD OF llIAKING PRESSURE VESSELS AND THE LIKE 3 Claims.

This invention relates to a method of manufacturing pressure vessels andthe like, particularly those capable of withstanding extremely highworking pressures and temperatures, and is a continuation in part of ourpending application, Serial No, 244,076, filed December 5, 1938, nowPatent No. 2,273,736.

As disclosed in the above noted application industry of today requiresvessels which are adapted to contain safely high pressures andtemperatures. In fact, many pressure processes require the use ofvessels in such size that the walls must be as much as six to eightinches in thickness. Manufacture :of such vessels is diflicult and anextremely expensive procedure. It is impractical to roll plates of thisthickness because shaping thereof produces uneven stresses between theinner and outer portions of the vessel wall. The inner portions of thevessel wall are placed in compression and the outer portions in suchextreme tension that the metal fractures because it is stretched to thepoint of failure. Forging and heat treatment must, therefore, beresorted to in forming metal sheets of the required thickness. The metalalso becomes so greatly distorted or deformed in the manufacturingprocedure that the internal stresses seriously weaken the vessel, and itis difficult to calculate safe working pressures that they maywithstand.

To solve these problems, attempts have been made to form vessels bywinding layer upon layer of sheet metal to build up walls of necessarythickness and then to form the layers in as nearly a homogeneous mass aspossible by heating and forging. However, the result is inaccurate andunsafe vessels are produced. Attempts have also been made to reinforcetubular articles such as pipe by wrapping the exterior with wire, thecoils being wound in side to side contact in a plurality of layers, butsuch articles will not withstand longitudinal bursting pressures and itis impossible to apply the desired tension in each wind for the reasonthat the wire would be stretched beyond its elastic limit, and if a wireof a size necessary to withstand the desired tension is used, internalstresses are produced in the wire similar to those produced when forminga vessel of thick metal plate, and, owing to the numerous number ofwindings which would be required, the vessel would be far moreinaccurate and entirely impractical especially due to the fact that thewindings will not reinforce the vessel in an axial direction.

It is, therefore, the principal purpose of the present invention toprovide a method of forming high pressure vessels wherein the internalstresses of the wall structure are controlled so that the stress issubstantially uniform throughout the thickness thereof and may be reliedupon to contain safely the working pressure for which the vessel isdesigned.

Other objects of the invention are to provide a method of forming alaminated vessel having a high strength weight ratio for safelycontaining a given pressure; to provide a method of vessel constructionby which the vessel may be accurately tested for leaks; and to provide amethod of forming laminated vessels wherein the laminations are securelyanchored to the heads of the vessel and each layer takes its part of theworking stresses transversely of the lamination and longitudinally ofthe axis of the vessel.

In accomplishing these and other objects of the invention, ashereinafter pointed out, we have provided an improved method ofprocedure as illustrated in the accompanying drawings, wherein:

Fig. 1 is a longitudinal section through a vessel constructed inaccordance with the present method.

Fig. 2 is a cross-section through the vessel on the line 2-2 of Fig. 1.

Fig. 3 is a similar section on the line 3-3 of Fig. 1 to betterillustrate attachment of a fitting to the wall thereof.

Fig. 4 is a perspective view of the inner shell or foundation of avessel having the heads welded thereto and showing th method of testingfor leaks, particularly the welds securing the heads to the shell.

Fig. 5 is a detail perspective View illustrating method of winding acontinuous metal ribbon on the tested shell whereby any predetermineddegree of tension may be produced in the respective layers according .tothe working pressure with which the tank is to be subjected.

Fig. 6 is a fragmentary section of the wall of the tank in the course ofconstruction, particularly illustrating the method 'of winding thelaminations.

Fig. '7 is a detail perspective view of a joint used in forming a ribbonof sufficient length to provide the required number of wrappings.

Fig. 8 is a detail fragmentary section of a modified form of vessel.

Referring more in detail to the drawings:

In carrying out our invention, we have discovered that when pressure isapplied within the interior of a thick wall vessel tending to enlargethe diameter thereof, the outer diameter is not increased perceptibly.This is accounted for in the fact that the inner portion of the wall iscompressed and the outer portion of the wall is placed in tension withthe result that the internal stresses seriously weaken the vessel and itis not capable of safely retaining the workin pressures for which thethickness was designed. We have also discovered that this action takesplace in a laminated wall, as heretofore used, with the result that thestresses imparted in the various layers cannot adequately perform theirpart in withstanding high internal pressures.

We have, therefore, found it essential to make use of stresses in ribbonlayers by varying the tension imparted thereto during wrapping so thatthe tension is controlled and varied according to the stresses which therespective layers must withstand to form a vessel of maximum strengthfor a given number of laminations and wall thickness. When thecylindrical wall of a vessel is formed merely by winding one convolutionupon another and the heads welded thereto, it is difficult to preventleaks, and when a leak does occur the pressure creeps out between thelaminations so that its origin cannot be determined from the outside ofthe vessel. To overcome this difficulty, we have adopted the principleof an automobile tire wherein an inner tube prevents leaks and the outercasing gives the required strength. We therefore make up an inner shellI by rolling a sheet of metal of a desired thickness to withstandtesting pressures, taking in consideration the inner diameter of thetank, the metal being sufficiently thin to permit ready fabricationthereof in cylindrical form and weld to the ends thereof heads 2 and 3which are preferably formed of solid metal and of desired thickness towithstand the internal working pressure of the completed vessel.

In the illustrated instance, the heads 2 and 3 are substantiallyhemispherical in form and have their inner circumference substantiallycorresponding to the inner circumference of the shell and the outercircumference corresponding to the outer diameter of the finishedvessel. The abutting faces 4 therefore project circumferentially of theouter surface of the shell and are tapered from the plane of the centersof curvature to facilitate welding, as later described. The heads 2 and3 are placed concentrically with the axis of the shell I and are weldedthereto as indicated at 5 and 6. If the shell is to be provided with afitting I, the fitting should be of proper thickness to withstand theinternal pressures of the finished vessel.

In the illustrated instance the fitting I is in the form of a ringhaving a central opening 3 registering with a corresponding opening 9 inthe shell. The outer periphery of the fitting may be rounded on suitablecurves, as at I0, and the terminal thereof flattened, as at H, to securetemporarily a closure plate l2. The face of the fitting secured to theshell is countersunk, as at l3, to receive welding M by which thefitting is attached to the shell. The portion of the fitting encirclingthe weld is preferably tapered, as at IE, to form an annular space toreceive a Welded metal l6 supplementing the inner weld I l.

The plate I2 is secured over the opening 8 by bolts l1 extendingtherethrough and secured in threaded sockets in the flattened face ofthe fitting. The plate !2 engages a T fitting l8, one terminal of whichis connected by a nipple I9 and the other with a central opening in theplate, and the other connections are respectively provided with a supplyline and a pressure gauge 21 whereby testing medium, such as a liquid,is admitted to the tank under a pressure registered by the gauge 2! totest the shell or foundation of the vessel against leaks prior tocompletion thereof. After testing, the plate I2 is removed and suitabletrunnions 22 and 23 are temporarily Welded or otherwise attached to theheads 2 and 3 in the axis thereof, as shown in Fig. 5, whereby the shellis rotatably supported in bearings 24 and 25 which are secured tosuitable supports 26 and 21. One of the trunnions, for example 22, is ofsufiicient length to be connected with any suitable power for effectingrotation of the shell. A metal ribbon is then prepared having a widthcorresponding. to the spacing between the heads of the vessel and ofsufficient length to provide the necessary number of convolutions toproduce a vessel of predetermined wall thickness. .One end of the ribbonis preferably skived and welded to the shell of the tank by a transverseweldas shown in Fig. 5. The ribbon is then placed in a gripping devicesuch as clamping bars 28 and 29, having angle-shaped inner surfaces 30and 3! cooperating with wedge plates 32 and 33 directly engaging theupper and lower surfaces of the ribbon. The wedge plates are drawn intoclamping engagement with the ribbon by draw-bolts 34 and 35 insertedthrough the ends of the clamping bars 28-29. The thicker portions of thewedges are arranged so that when pulling pressure is applied to the barsin a direction away from the welded end of the ribbon, this pressureacts to enhance gripping action of the wedges to prevent slippagebetween the bars and ribbon. The ends of the bars are suitably connectedwith hydraulic cylinders 36-41 through rods 38-39 whereby variabletensions are applied in the ribbon through control of the fluid pressuremedium used in the respective cylinders as the ribbon is being Wound onthe shell. The pressures indicated by the gauges 40 and 4| which i areconnected with the respective cylinders relate to the tension beingmaintained on the ribbon. While the tension is maintained on the ribbon,the shell or foundation is being rotated to wrap the I ribbontherearound.

In the tank illustrated it is necessary to cut an opening 32 in eachconvolution so that the fitting will pass therethrough, permitting theconvolutions to engage each other closely, whereby frictional contact ofone convolution or layer upon the other prevents unwinding thereof andtherefore maintains the imparted tension. If desired, the ribbon may beprovided With welding apertures 33 whereby one convolution is welded tothe other as indicated at 44. A sufiicient number of convolutions iswound on the shell so that the peripheral face of the final convolutionor layer registers with the circumferential edges of the heads. Duringreadjustment of the bars 28 and 29, when the hydraulic mechanisms havecome to the limit of their stroke,tension may be maintained on theribbon by a similar mechanism, adjustable weights, or the like. When thewinding is complete the free edge of the ribbon is preferably skived, asindicated at 45, and welded to the underlying convolution by welding 46.

In order to provide a welding space between the convolutions and theheads, the side edges of the ribbon are so shaped that when wound on theshell they will lie on an angle corresponding to the angle of the headfaces 4 to form a welding space in which a welding material is depositedas indicated at 41 and 48. Welding material is also filled in around thefitting as indicated at 49.

In tanks requiring longer ribbons than the length of sheets obtainable,they may be formed of a series of sheets preferably having ends cut on abias, as shown at 50 in Fig. 7, whereby the joint extends spirallyrelatively to the shell and the gripping action of the upper and lowersheets supplements the strength of the weld. In extremely long tanks,two or more ribbons of substantial width may be wound on the shell andwelded together in the manner above described.

In order to avoid skiving or feathering of the inner edge of the sheet,or that edge attached to the shell I, the edges of the shell, whensecured together, may be offset as indicated at 5|, Fig. 8. The edge 52of the ribbon may be abutted against the offset and welded as shown.

In order to give a better understanding of the variable or differentialtension applied to the respective convolutions to produce a vessel ofmaximum strength, the operations of constructing a vessel of specificsize are now to be described. Assuming that the vessel has a A" shellrolled to a 7" radius for producing a vessel of 14" inside diameter, andassuming that a ribbon of thickness and of substantial width, forexample the full width between the heads of the shell, is to be wound ineight convolutions about the shell to produce an outside dimension of8%," radius or 17%; in diameter, the steps are carried out as follows:

For calculations, a working pressure within the tank may be assumed tobe 3,000 pounds per square inch. The A. S. M. E. Code gives thefollowing stress in the above mentioned vessel.

Stress=l5.75 3000/2 1.75=l3,500 lbs. per sq. in

The stress in the above vessel using the more exact equation derived andapplicable to shells relatively thick compared to the diameter (Strengthof Materials case, Longmans, Chap. XXVIII) Where f1=inner radius ofvessel rz=outer radius of vessel r=radius at point where stress is to befound p internal pressure s=stress caused by this pressure Substitutingin the above formula we get stress at inner radius where r=r1 Stress atouter radius where r=rz 13,680 lbs/in.

s 10,700 lbs/in? thickness of the wall are made substantially uniform.

In constructing the above mentioned vessel, the shell I is formed byrolling a metal plate 5 to 14 inside diameter, welding the seamandapplying the heads 2 and 3, after which the vessel is tested forleaks. The trunnions 22 and 23 are temporarily connected with the headsand mounted in the bearings 24 and 25. A metal ribbon of plate and ofsuflicient length to form eight convolutions or windings about the tankis prepared with or without the openings 43. If a ribbon of sufficientlength is not available, plates may be welded together, as shown in Fig.'7, to provide the desired length. One end of the ribbon is thenpreferably skived and attached to the shell along a tangent parallelwith the axis of the trunnions and in a position so that the side edgesof the ribbon will cooperate with the faces 4 of the heads to form thewelding grooves. The clamping bars 28 and 29 are attached at a suitablepoint on the ribbon relatively to the stroke of the rods 38 and 39 andfluid is admitted to the cylinders to apply tension in that portion ofthe ribbon between the bars and shell.

The desired tensions to be imparted in the ribbon so as to producesubstantially uniform ultimate tensions in all the convolutions may becalculated as set out in the following table:

The headings in the above table designate the thickness of the shell andthe convolutions wound therearound. The figures in column one designatecompression forces on the inner shell which vary from -598 pounds withthe first convolution to 2194 pounds after the eighth or finalconvolution has been applied. The first figures in the columns designatetension in pounds per square inch of width maintained in the ribbon asthe convolutions are formed. The subsequent figures in these columnsdefine the tension maintained in the convolution with each wind. Forexample, after the second convolution has been wound over the first,maintaining a tension of 510 pounds per inch of width in the secondconvolution, the tension of the first convolution has been reduced from598 to 512 pounds. After the third convolution has been formed thetension in the first convolution has been reduced to 448 pounds andtension in the second convolution has been reduced to 446 pounds. Itwill be noted that each reduction in winding tension averages about 20%less than the previous reduction. Thus the tensions of the convolutionsafter the final one has been applied are the figures in the bottom ofthe columns. It will be noted that these figures are, for practicalpurposes, of similar relative magnitude. For example, the tension in iThe important requirement is that the tension applied during the windinof the outer convolutions is reduced from the tensions employed inwinding the first convolution so that the windings result insubstantially uniform stresses throughout the wall thickness of thevessel, thereby avoiding the uneven stresses which occur when formingvessels of solid plate metal of sub stantial thickness.

Continuing with the construction of the vessel in accordance with theabove table, the pressure in the cylinders 3'6 and 3'! will be adjustedso that as the shell is rotated to wrap the first wind or convolutionthe tension applied is 598 pounds on the gauges, which produces acompression force of 598 pounds in the shell. If the perforations 43 areprovided in the ribbon, the wound convolution may be Welded to the shelltherethrough, and if the shell is provided with a fitting l a suitableopening 42 i provided in the ribbon to ass the fitting. Upon completionof the first convolution the pressure in the cylinders is adjustedrelative to rotation of the shell for reduc ing the tension imparted inthe ribbon to 510 pounds as designated in the third column, theconvolution being afiixed in the same manner as the first convolution.After wrapping the second convolution the tension in the shell is 1022pounds, and the tension in the first convolution 512 pounds. Thesucceeding convolutions are wound in like manner, reducing the tensionfor each succeeding convolution to 446, 395, 355, 324, 298 and 2'75respectively, as shown in columns four, five, six, seven, eight and nineof the table. After th final Wind, the free end of the ribbon i weldedalong the edge thereof to the preceding convolution.

Attention is directed to the fact that if the perforations 43 areomitted, the frictional contact of one convolution on the other willprevent slipping and maintain the desired tensions. This frictionalcontact may be supplemented by welding the edges of the ribbon, or theedges may be finally welded by filling in the welding spaces at theheads of the vessel. During winding of the ribbon it may be necessary todisconnect and reengage the clamping bars, however, tension ismaintained on the ribbon during this operation as previously pointedout. After completing the application of the ribbon, the trunnions arere- Initial Stress due Total Radius stress to pressure stress Asmentioned, the above table designates stresses. The first columndesignates the radius of the respective convolutions. The second columndenotes the initial stress on the respective convolution due to thewinding tension, and the third column designates stress when internalpressure is applied in the tank. The final column denotes the totalstress. The figures in column two are obtained by dividing the tensionsin the last line of the first table by the thickness of the variouconvolutions. Column three is calculated by applying the above equation,and figures in the last column ar obtained by adding algebraically thefigures in columns two and three.

It is to be understood that the above calcula tions for a specific tankor vessel are merely illustrative of the variable stresses impartedduring Winding of the convolutions and these stresses may be variedtherefrom to provid a tank suit able for any given purpose. However, thetension imparted during winding the convolutions is reduced in valuefromthe inner to the outer convolutions and preferably so that theultimate tensions in the respective convolutions are uniform orsubstantially uniform.

From the foregoing it is apparent that We have provided a method ofproducing a laminated vessel wherein the convolution are maintainedunder a predetermined initial stress calculated to give maximum strengthand to withstand.

safely the working pressures for which the tank is designed.

What we claim and desire to secure by Letters Patent is:

1. The method of forming the wall of a vessel capable of withstandinghigh internal pressure including, winding a metal sheet of substantialwidth in continuous successive convolutions one directly upon anotherwith the face surface of one convolution in frictional contact with thenext preceding convolution and with the edges of the sheet insubstantial registrywnsion in said sheet substantially uniformly mammthesheet at the time of winding said convolutions, selectively andprogressively reducing the winding tension in each convolution, eachreduction in winding tension being on an average of about 20% less thanthe previous reduction in winding tension so that the ultimate tensionsand stresses in all the convolution are substantially uniform, andwelding at least the final convolution to the preceding convolution.

2. The method of making laminated tubular walled vessels capable ofwithstanding high internal pressure including, forming a tubular shell,winding a metal sheet of ubtantilwidth in continuous successiveconvolutions about the shell one directly upon and continuous with theother with the face surface of one convolution in frictional contactwith th next preceding convolution and with side edges of the sheet insubstantial registry, yglriggim ig in said sheet uniformly e r t 1 idt rsa dsiiieet'afthe time of Winding said convolutions, selectively andprogressively reducing the winding tension in each convolution, eachreduction in winding tension being on an average of about 20% less thanthe previous reduction in winding tension 50 that the ultimate tensionsand stresses in all convolutions are substantially uniform, and weldingeach successive convolution to the previous convolution progressive withthe Winding.

3. The method of forming the wall of a vessel capable of withstandinghigh internal pressure including, winding a sheet of substantial widthin continuous successive convolutions one directly upon another with theface surface of one convolution in frictional contact with the next preceding convolution and with the edges of the sheet in substantialregistry, applying tension in said sheet substantially uniformlyparallel with the axis of the winding at the tim of winding saidconvolutions, selectively reducing the winding tension in said sheetafter the winding of each convolution in an amount to produce anultimate tension in each of the previous convolution substantially thatof the tension in effect in said sheet at the time of winding the finalconvolution whereby the ultimate tensions in all of the convolutions aresubstantially all similar in magnitude and so that the stresses in thewall of the completed vessel are substantially uniform throughout thethickness thereof, and securing at least the final convolution to thepreceding convolution.

GWYNNE RAYMOND. MERL D. CREECH. RALPH L. FEAGLES.

